Former Dallas Cowboys defensive end Marshawn Kneeland has been diagnosed with stage 1 chronic traumatic encephalopathy (CTE).
Kneeland , who died by suicide at 24 years old in November 2025, was diagnosed posthumously by researchers at Boston University's CTE Center, according to a press release from the Concussion and CTE Foundation. Kneeland was in his second professional season with the Cowboys when he died. The press release noted that he had been playing tackle football since he was seven years old.
"Unfortunately, I was not surprised to find CTE in the brain of Mr. Kneeland, because we have found this progressive brain disease in nearly half of the athletes we've studied who have died before the age of 30," said Dr. Ann McKee, director of the Boston University CTE Center and chief of neuropathology for the VA Boston Healthcare System, in a statement.
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CTE can only be diagnosed after death, with no specific symptoms tied to the disease present while a victim is alive. However, symptoms with possible ties to CTE include memory loss, impulsive behavior and depression.
"While this diagnosis does not change the tragedy of his passing, it provides important context about some of the struggles he may have been facing," Kneeland's family said in a statement. "We share this information to help people understand what NFL and other high contact sport athletes might be struggling with.
"Raising awareness is important to us. We continue to remember Marshawn with compassion for the person he was, rather than defining him by the final moments of his life."
Kneeland died early in the morning on Nov. 6, according to statements from the Cowboys and Jonathan Perzley , his agent and friend. He was 24.
The Frisco, Texas, Police Department released a statement on Nov. 6 that they responded to a request to assist the Texas Department of Public Safety to locate a car that had evaded state troopers during a pursuit. Troopers discovered the car crashed on Dallas Parkway, with signs that its driver – later identified as Kneeland – apparently fled on foot.
According to the statement, Kneeland was found deceased early in the morning on Nov. 6. The Collin County Medical Examiner's Office later determined that Kneeland died by suicide.
CTE, which stands for chronic traumatic encephalopathy, is a degenerative brain disease that destroys nerve cells in the brain, according to the Mayo Clinic .
It is linked to repeated traumatic brain injury, such as concussions, and has been found in many former boxers, NFL players and military combat veterans after their deaths.
CTE can only be diagnosed after death, with no specific symptoms tied to the disease present while a victim is alive. However, symptoms with possible ties to CTE include memory loss, impulsive behavior and depression. According to the Mayo Clinic, any symptoms that form as a result of CTE form over several years following multiple instances of traumatic brain injury. They will not necessarily be present immediately after a concussion or other similar injury.
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Belcher played for the Chiefs for three full seasons and played in 11 more games for Kansas City in a fourth season before he killed his girlfriend, then himself, in December 2012. ESPN reported in 2014 that a medical examiner determined Belcher's brain had signs of CTE.
Cross was a two-time Pro Bowler who played in the NFL for nine years. In his rookie season, Cross earned the nickname "Paper Head" for the sheer number of concussions he suffered in the 1961 season alone, according to a 2018 interview he had with the Philadelphia Inquirer. Cross went on to become the first Black sports analyst on national TV after his career.
He was diagnosed with a form of dementia shortly before his death, which he believed could be attributed to CTE. He donated his brain to the Boston University CTE center, where it became one of the 345 from former NFL players diagnosed with the disease.
Dobler played 10 years in the NFL and appeared in the Pro Bowl for three consecutive years from 1975 to 1977. After he died in February 2023, he donated his brain to Boston University, where he was posthumously diagnosed with CTE.
Henry played for the Cincinnati Bengals for five years – between 2005 and 2009 – before his death in December 2009. The wideout fell out of the back of a moving truck during a domestic dispute and a hit to his head led to his death. Six months later, the Brain Injury Research Institute of West Virginia announced Henry had developed CTE prior to his death.
Hernandez played three years for the Patriots starting in 2010. Four years after he was imprisoned for the murder of Odin Lloyd, Hernandez committed suicide in his cell. After his death, Boston University diagnosed the former tight end with CTE. A Hernandez family lawyer said while announcing his diagnosis that the case of CTE was "the most severe case they had ever seen in someone of Aaron's age."
A former second-round pick by the then-San Diego Chargers in 2005, Jackson played 12 years in the NFL and made three Pro Bowls by the time he retired in 2016. He died in 2021, aged 38, from chronic alcohol use, according to a medical examiner and was diagnosed with CTE by Boston University's CTE Center.
Long played his entire eight-year career for the Pittsburgh Steelers. In 2005, 14 years after his final season, he committed suicide by drinking an entire gallon of antifreeze shortly after an indictment for arson and fraud charges. His autopsy, performed by neuropathologist and CTE discoverer Bennet Omalu, revealed that he had the degenerative brain disease.
Seau's career spanned nearly three decades – from 1990 to 2009 – and was marked by numerous accolades, including first-team All-Pro recognition six times, 12 consecutive Pro Bowl seasons and a Walter Payton Man of the Year award. His 20-year career included two Super Bowl appearances: one with the Chargers in Super Bowl 29 and another with the Patriots in Super Bowl 42.
Seau committed suicide in 2012, and his family donated his brain tissue to the NIH's National Institute of Neurological Disorders and Stroke. A year later, they revealed the NIH had found signs of CTE.
The linebacker was posthumously enshrined into the Pro Football Hall of Fame in 2015.
By the end of Thomas's nine years with the Denver Broncos, he had risen to second in all-time receiving yards in the team's history. He won a Super Bowl with Denver after the 2015 season and played four more years that included brief tenures with the Houston Texans and New York Jets. He died in December 2021 from what police called a "medical issue" that stemmed from a 2019 car crash. His brain tested positive for signs of CTE after its donation to Boston University.
Wycheck was an 11-year NFL veteran who earned three Pro Bowl nods during his career and is a member of the Titans/Oilers Ring of Honor. He was the Titans' leading receiver for three years (1999-2001) and was the player who threw the famous lateral pass in the "Music City Miracle" play that led Tennessee to a playoff win over the Buffalo Bills. Wycheck died in 2023 after falling and hitting his head. In January 2025, ESPN reported that his family confirmed Wycheck had been diagnosed with CTE after his death.
If you or someone you know needs mental health resources and support, please call, text or chat with the 988 Suicide & Crisis Lifeline or visit 988lifeline.org for 24/7 access to free and confidential services.
This article originally appeared on USA TODAY: Marshawn Kneeland, Cowboys player who died by suicide at 24, diagnosed with CTE
